Apparatus for testing lubricants



Jan. 14, 1958 A. D. SHELLARD ETAL APPARATUS FOR TESTING LUBRICANTS Filed April 19, 1956 R i l 10 i s *2. VIIII'IIIII I INVENTORS ARTHUR DONALD SHELLARD ALLAN LINDSAY TEMBY THEI AGENT United States Patent 2,819,611 APPARATUS non TESTING LUBRICANTS.

Arthur Donald Shellard, Wrexham, Wales, England, and

Alan Lindsay Temby, Eaglemont, Melbourne, Australia, assignors to Shell Development Company, New York, N. Y., a corporation of Delaware Application April 19, 1956, Serial No. 579,374

Claims priority, application Great Britain April 26, 1955 3 Claims. (Cl. 73-64) This invention relates to an apparatus for testing hydrocarbon oils, particularly hydrocarbon lubricating oils, to provide quantitative information regarding their evaporation characteristics at elevated temperatures and to the application of such a method of testing to the control or improvement of the manufacture of hydrocarbon oils.

Various physical properties of oils and oil compositions, such as viscosity, pour-point, flash-point, and the like, have proven to be unreliable as measures of their lubricating properties. In many cases such products, which apparently possess satisfactory physical requirements of the character indicated are markedly poor in actual performance in the operation of engines, gears, or the like. Various means have been developed to determine the lubricating quality of mineral oils, such as described in U. S. Patents 2,065,625; 2,174,021 and 2,228,671. However, these methods still leave much to be desired to insure that the oil will possess certain properties which are required in various applications.

It has now been discovered that hydrocarbon oil properties which are determinative for particular uses can be quickly and reliably evaluated and controlled by determining the evaporation characteristic of the hydrocarbon oil, and maintaining it between limits predetermined experimentally according to the intended use of the hydrocarbon oil.

Since hydrocarbon oils invariably comprise mixtures of hydrocarbons of differing volatilities, the term evaporation characteristics is employed herein in preference to volatility or rate of evaporation to denote the manner in which the mass of a given sample of the hydrocarbon oil changes with time as the result of the removal of components thereof by evaporation, and, as will be apparent from the description which follows, a basis has now been established for expressing the evaporation characteristics of a hydrocarbon oil in a quantitative manner.

According to the present invention a means of testing a hydrocarbon oil by determining its evaporation characteristics at an elevated temperature comprises suspending a droplet of the oil in a stream of hot inert gas, the temperature and rate of flow of which is substantially constant, and determining the change in size of the droplet, or a parameter thereof, with time.

The term inert gas is used herein to denote a gas which, at the aforesaid elevated temperature, does not cause any substantial change in the chemical nature of the oil in the droplets. Thus air is not usually suitable because of its oxidizing effect on the oil.

The inert gas is preferably superheated steam, although nitrogen or carbon dioxide are also suitable.

The change in size of the suspended oil droplet with time is preferably determined by determining the volume of the droplet (or a parameter thereof, such as the volume of a magnified optical image of the droplet) from time to time during the course of the test, andexpressing the results as a percentage of the volume of the droplet at the commencement of the test. Each of the resulting ice values-hereinafter referred to as the volume percent at time t and temperature T, i. e. V. percent (t, T), is a quantitative expression of the evaporation characteristics of the oil at the elevated temperature T. Usually a series of such values is obtained at the temperature T, forexampic, at 5 minute intervals over a period of 20 minutes. If desired a standard elevated temperature (T), for example, 315 C. in the case of steam-cylinder oils and 150 C. in the case of motor oils, may be adopted when the test is used for routine control on a manufacturing scale.

, An approximation of the true volume of the oil droplet which is sufliciently accurate for most purposes may be obtained by cubing the width of the droplet. The width may be measured directly, for example, by means of a traveling microscope or an eyepiece containing a graticule: alternatively the width of a magnified optical image of the droplet can be measured, for example, by forming the image on a screen and measuring its width by means of a scale. In order to allow for the slight elongation of the droplet induced by the inert gas stream, the width of the droplet at the commencement of the test should be determined with the droplet in the gas stream and not in still air. With results expressed in accordance with this approximation, repeat tests at the same temperature, run either consecutively or some weeks apart with droplets of the same oil, can give results which do not differ by more than :1% over the period (usually 20 minutes) of the test.

It will be appreciated that the change in size of the oil droplet may also be determined by determining the change in weight of the droplet during the test and the evaporation characteristics expressed in terms of weight percent.

The evaporation characteristics of a lubricating oil for use as a steam-cylinder or turbine oil are conveniently determined in accordance with the invention by suspending a droplet of the oil in a steam of superheated steam at for example 315 C. By repeating the test at a m n ber of differentelevated temperatures information can be obtained regarding the performance of the oil in steam atmospheres over a wide temperature range. A

Since suflicient quantitative information regarding the evaporation characteristics of an oil at aparticular elevated temperature can usually be obtained in well under an hour, it will be appreciated that the method of testing of the present invention is eminently suitable for application as a routine test method for controlling the qnality of the oil during its manufacture or blending.

Consequently, the present invention also provides a means of controlling the quality of a hydrocarbon oil during its manufacture or blending, which comprises periodically suspending a droplet of the oil being produced in a stream of hot inert gas, the temperature and rate of flow of which is substantially constant, and determining the change in size of the droplet, or a parameter thereof, with time, and, if and when necessary, adjusting one or more of the conditions of the process of manufacture or blending to maintain said change within predetermined limits.

Hitherto, information as to the evaporgtion characteristi'cs of a steam-cylinder oil at an elevated temperature has been obtained by steam-distilling a sample of the Dil at say 350 C. and periodically determining the pergentage of oil in the condensate and plotting this against the percentage of oil distilled. This is a long and tedious procedure and in practice it is usually discpntinned when the rate of distillation of the oil falls to 1% of the total condensate. Generally when a first quality. steam-cylinder oil for use with highly superheated steam is steamrdistilled in this way, less than of the ,oilis distilled and sincetheoperation may take a full working day Qreven longer, it is hardly suitable for use as a control test on a manufacturing scale.

Moreover, the steam-distillation test hitherto employed cannot usually provide much information about the heavy ends of the oil, since with good quality steam cylinder oils these heavy ends are left over as a liquid or semi-solid residue. This difiiculty does not arise with the test method of the present invention since it is possible to continue evaporation of the suspended oil droplet until a solid residue is obtained, the amount and nature of which residue can provide useful information regarding the deposit-forming characteristics of the oil in a steam atmosphere.

The present invention also provides apparatus for use in determining the evaporation characteristics of a hydrocarbon oil at an elevated temperature, comprising means for producing a stream of hot inert gas of substantially constant predetermined temperature and rate of flow, means for suspending an oil droplet within said gas stream and means for continuously or periodically indicating or determining the size of the suspended droplet, or a parameter thereof.

When steam is employed as the inert gas, the apparatus conveniently comprises a steam boiler, superheater as sociated therewith, said superheater having an outlet orifice adapted to provide a stream of superheated steam of substantially stable fiow characteristics in the region of the suspended droplet, and means for indicating the temperature of the steam passing over said droplet.

Preferably in such a case the boiler is a flash-steam boiler having means for feeding Water (preferably pure, e. g. distilled water) thereto at a predetermined substantially constant rate, and the superheater is electrically heated and has a steam diffusing element between its electrical heating element and its outlet orifice. The temperature of the steam passing over the droplet is conveniently determined by disposing a temperature-sensitive element in the path of the gas stream substantially immediately beyond the droplet.

An apparatus in accordance with the invention for determining the evaporation characteristics of a lubricating oil will now be described by way of example and with reference to the accompanying drawing, in which:

The figure shows diagrammatically the general layout of the apparatus.

The apparatus comprises essentially a flash-steam boiler which supplies steam to a superheater 6 having a nozzle 7 from which superheated steam issues in the form of a jet or stream. A droplet 8 of the oil whose evaporation characteristics are to be determined is suspended in the steam jet as will be described.

The boiler 5 is in the form of a small drum having a funnel-shaped steam outlet 9 in its side wall: it also has a water inlet 10 terminating in a jet H and adjustably supported in a tube 12 welded to the upper part of the boiler. The tube 12 carries a disc 13 for deflecting heat rising from the burner 14. The bottom of the boiler 5 is covered by a layer of well-teased, long-fiber asbestos 15 to promote smooth steaming and the burner 14 is surrounded by a draft screen 16. The size of the jet 11 is such that a continuous stream of distilled water is supplied to the boiler 5 from a constant level device 17.

The superheater 6 comprises an outer shell 18 within which is disposed a silica tube 19. The steam outlet 9 of the boiler 5 ends in a disc 20 having an axial aperture 21 and two coaxial cylindrical portions 22, 23 forming respectively a steam outlet passage and a connecting sleeve for attachment to the outer shell 18 of the superheater 4, pins 24 on the sleeve 23 co-operating with slots (not shown) in the shell 18 to form a bayonet connection. The space between the sleeve 23 and the shell 18 is packed with asbestos 25 to provide a steam-tight joint. A second silica tube 26 supporting an electrical heating element 27 is disposed coaxially within the tube 19 by spacers (not shown) and carries a steam-distributing baffie 28 at its end nearest the boiler 5. At the downstream end of the heating element 27 is a diffuser comprising a removable sleeve 29 containing, for example, six wire mesh grids 30 which serve to stabilize the temperature and flow characteristics of the superheated steam. Beyond the diffuser is the removable nozzle 7 containing an axial orifice 31, the inner surface 32 of the nozzle being shaped to provide a steam jet 33 leaving the orifice 31 which has streamline flow characteristics in the region of the suspended oil droplet 8.

The oil droplet 8 is supported by the lower end of a glass fiber 34 carried by an adjustable screw 35 which permits adjustment of the position of the droplet 8 relative to the steam jet 33. A thermocouple element 36 is provided in the path of the steam jet 33 on the downstream side of the droplet 8 and is connected in an appropriate circuit (not shown) for determining the temperature of the steam jet in the region of the droplet 8.

A draft screen (not shown) is provided to exclude drafts from the droplet 8, the draft screen having two opposed apertures for the passage of a light beam from a lamphouse 37 to a projection lens system 38, the light path being so disposed as to include the droplet 8. The lens system 38 is so adjusted in relation to a screen 39 disposed at right angles to the light path as to form a magnified image 40 of the droplet thereon. A scale 41 is provided on the screen 39 for measuring the size of the image and observing its rate of change.

The electric heating element 27 of the superheater 6 is connected to a suitable electric power source through .an adjustable resistance 42 which provides means for bringing the temperature of the steam jet to the value required for the test. Before the apparatus is used it should be allowed to warm-up and adjust to steady steam jet temperature conditions as determined by the setting of the resistance 42.

The fiber 34 on the lower end of which the oil droplet is supported is preferably a glass fiber 0.04:0.005 mm. in diameter, which is substantially without taper over the last 5 mm. at least of its lower end. A deflecting plate is placed temporarily in front of the nozzle 7 while a droplet is being formed on the tip of the fiber 34, the latter operation being conveniently efiected by dipping a fine glass fiber in the oil to be tested and transferring a suitable drop onto the fiber 34. The size of the droplet 8 is conveniently such that its width in still air is 0.73:0.01 mm. and if the size of the droplet formed initially on the fiber 34 does not fall within this range it is. preferably increased or decreased until it does.

Since very small amounts of water in or on the surface of the oil droplet can cause the droplet to disinte-- grate violently as soon as the steam jet is turned onto it,

care should be taken to insure that there is no cloud of condensed steam around the droplet while it is being formed on the fiber 34.

The invention is illustrated by the following examples:

EXAMPLE I It was necessary to compare the evaporation characteristics of two 1000 second, Redwood I at F. high viscosity index oils, one of which had been clay-treated. The evaporation characteristics of each oil were determined at 220 C., 270 C. and 315 C., using the apparatus described above. For each of these temperatures two determinations were made with the oil droplet temperature slightly above and slightly below the required temperature respectively, the evaporation characteristics at the required temperature being obtained by interpolation.

It was found that the treated and untreated oils had practically the same evaporation characteristics over the temperature range 220 C.-315 C., as will be apparent from the data in Table I.

Information was required as to the viscosity to which a lubricating oil produced from a La Paz crude by a solvent extraction process would have to be controlled in order to possess evaporation characteristics comparable to those of a straight run lubricating oil (oil A) produced from a Pennsylvania crude. The highest viscosity lubricating oil then being produced in the solvent extraction plant was oil B which had a viscosity of 650 sec. Redwood I at 140 F. The evaporation characteristics of oils A and B were determined at 315 C. using the apparatus described above and the volume percent after 20 minutes of these oils was found to be 21 and 9, respectively. Two further oils (C and D) having viscosities of 1184 and 1450 seconds Redwood I at 140 F., respectively, were then produced in the solvent extraction plant and their evaporation characteristics determined. It was found that the volume percent of oil D after 20 minutes was 21, i. e. the same as that of oil A. The full results obtained are shown in Table II.

Table 11 Percentage volume of droplet remaining atten- 011 5 min. min. 15 min. min.

EXAMPLE III A lubricating oil, comprising a blend of a SAE 10W base oil with a bright stock of 650 seconds Redwood I at 140 F. viscosity, was required having evaporation characteristics comparable to those of a previously made SAE 10W grade motor oil which was adopted as a reference oil. The evaporation characteristics of the reference oil, the SAE 10W base oil and blends of the latter with 10% and 20% of the above-mentioned bright stock were determined at 150 C. using the apparatus described above and the results obtained are shown in Table HI.

It will be seen that whereas the blend of SAE 10W base oil+l0% bright stock had a V. percent (20 min., 150 C.) greater than that of the reference oil, the blend of SAE 10W base oil+20% bright stock had evaporation characteristics which in general equal or surpass those of the reference oil over the whole of the 20 min. period of the test.

In the subsequent production of the 20% blend, the evaporation characteristics of a sample of the blend being produced were determined from time to time and when necessary the proportion of bright stock in the blend was altered slightly on either side of the 20% level to maintain the evaporation characteristics substantially the same as those quoted in the last line of Table III.

The present invention has wide application and may be used in connection with oils intended for various uses and oils derived from various sources, including distillate oils and residual oils, and fractions thereof, derived from asphaltic, naphthenic or paraffinic base crude oils. It is applicable to various manufacturing operations, whether physical or chemical changes are involved, or both, including physical separations, such as distillation, extraction, dewaxing, etc. and physical combinations, such as blending oil fractions or oils with oil additives, and chemical changes, such as involved in acid treatment, synthesis of polymer oils, and the like.

We claim as our invention:

1. An apparatus for use in determining the evaporation characteristic of a hydrocarbon oil at an elevated temperature, comprising heating and flow control means for producing a stream of hot inert gas of a predetermined temperature and rate of flow, suspension means for positioning an oil droplet within said gas stream and optical means for determining the size of the suspended oil droplet at time intervals.

2. Apparatus as claimed in claim 1, comprising a steam boiler having a discharge port, a superheater in communication therewith, said superheater having an outlet orifice adapted to provide a stream of superheated steam of substantially stable flow characteristics in the region of the suspended droplet, and thermal responsive means for indicating the temperature of the steam passing over said droplet.

3. Apparatus as claimed in claim 1, comprising a flashsteam boiler, conduit means for feeding water thereto at a predetermined substantially constant rate, an electrically-heated superheater in communication with said steam boiler having a steam-diffusing element between its electrical heating element and its outlet orifice, and a temperature-sensitive element disposed in the path of the gas stream substantially immediately beyond the position of the suspended droplet.

References Cited in the file of this patent UNITED STATES PATENTS 1,014,139 Freeman Jan. 9, 1912 1,967,424 Nevitt July 24, 1934 FOREIGN PATENTS 100,676 Great Britain June 22, 1916 615,333 Germany July 3, 1935 

1. AN APPARATUS FOR USE IN DETERMINING THE EVAPORATION CHARACTERISTIC OF A HYDROCARBON OIL AT AN ELEVATED TEMPERATURE, COMPRISING HEATING AND FLOW CONTROL MEANS FOR PRODUCING A STREAM OF HOT INERT GAS OF A PREDETERMINED TEMPERATURE AND RATE OF FLOW, SUSPENSION MEANS 